Thread cutting arrangement on lock stitch sewing machines

ABSTRACT

The invention concerns an arrangement for cutting off the sewing threads on lock stitch sewing machines that are equipped with a shuttle rockably driven in a stationary guide means and having a support that is pivotable about a vertical axis upon which a shuttle thread cutter is disposed and behind the same a needle thread cutter with spacing therebetween. In this connection the cutters effect a first rocking step for seizing the threads. Upon completion of a further stitch forming operation whereby the needle thread loop places itself about the needle thread cutter, the threads are severed during a second rocking step.

United States Patent [191 Hager et al.

[ 1 July 15, 1975 THREAD CUTTING ARRANGEMENT ON LOCK STITCH SEWING MACHINES [75] Inventors: Walter K. Hager; Willi Klein. both of Kaiserslautern, Germany [73] Assignee: Pfaff lndustriemaschinen G.m.b.II.,

Kaiserslautern, Germany 22 Filed: Apr. 8, 1974 21 Appl. No.: 458,574

Primary Examiner-Alfred R. Guest Attorney, Agent, or FirmRobert l'l. Jacob [57] ABSTRACT The invention concerns an arrangement for cutting off the sewing threads on lock stitch sewing machines that [30] Foreign Application Priority Data are equipped with a shuttle rockably driven in a sta- Apr 12 1973 Germany 7313848 tionary guide means and having a Support that is pivotable about a vertical axis upon which a shuttle 52 us. (:1. 112/252 thread Cutter is dislwsed and behind the Same a needle 51 lm. c1. DOSB 65/00 thread Cutter with Spacing therebetween- [58] Field of Search l12/65 67 129 130 189 nection the cutters effect a first rocking step for seiz- 2 ing the threads. Upon completion of a further stitch forming operation whereby the needle thread loop [56] References Cited places itself about the needle thread cutter, the

UNITED STATES PATENTS threads are severed during a second rocking step.

2,163,994 6/1939 Fischer 112/252 1 Claim, 4 Drawing Figures PATENTEU JUL 1 5 975 SHEET Fig. 3

THREAD CUTTING ARRANGEMENT ON LOCK STITCH SEWING MACHINES BACKGROUND In sewing machines having a central bobbin shuttle driven in a stationary guide, arrangements are known for thread cutting which include a support that is pivotable about a vertical axis which is connected with a toothed gear. Two individually operable electromagnets that are disposed alongside one another serve as drive means, the draw bars of which are connected with a draw bar cooperating by way of a double lever with the toothed gear. On the support a flat cutter is mounted for the shuttle thread which is equipped with a low upwardly directed cutting lip. A cutter of flat construction for the needle thread is disposed on the support extending in the direction of operation behind the cutter for the shuttle thread with space therebetween and which has a downwardly directed elongated cutting finger. The guidance of the central bobbin shuttle is adapted to the means for the thread cutting in a manner that directly behind the stopping finger of the bobbin capsule a free space is provided for the unimpeded movement of the cutting finger of the cutter for the needle thread.

The cutters effect two swivel movements to seize and sever the threads. During the first swivel steps the cutter for the shuttle thread is swung past underneath the stitch hole, seizes the shuttle thread and pulls the same out laterally. Simultaneously the cutting finger of the cutter for the needle thread moves behind the stopping finger of the bobbin capsule and comes to rest directly behind this stopping finger. Thereupon a stitch forming operation is effected, during the course of which the needle thread loop slips first onto the stopping finger and finally on the cutting finger upwardly. Now the second pivoting step is effected whereby the threads that pull themselves taut are severed by the edges of the cutters.

An arrangement of this type for cutting threads can only be employed with sewing machines having central bobbin shuttles, but not with different shuttles as, for example, with a long beak shuttle that does not have a bobbin capsule and thus also no retaining or stopping finger. Without the stopping finger upon which the needle thread loop slides up as upon a guiding element and from which it slides on under controlled guidance upon the cutting finger of the needle thread cutter, no assurance would be provided that the needle thread loop after being guided about the long beak shuttle that now moves upwardly more or less without control actually slings itself around the cutting finger that stands still.

A further shortcoming of such an arrangement for thread cutting exists as already mentioned in that the guidance of the central bobbin shuttle has to be changed to a considerable extent with respect to the normal construction, so that the cutting finger can be moved unimpededly past the finger retaining the capsule.

Accordingly, it is an object of the invention to provide for the elimination of the aforementioned shortcomings for sewing machines having a shuttle which may be a central bobbin or long beak shuttle, a thread cutting means with a shuttle thread and a needle thread cutter, where the two cutters which effect two swinging or rocking steps for seizing and severing the threads remain always outside of the path of movement of the shuttle and outside the extent of the area of the normally shaped guidance of the shuttle, and where the needle thread loop is introduced by means of a guiding element to the needle thread cutter. In accordance with the invention this problem is solved in that the needle thread cutter is provided with a guiding finger for the needle thread loop that comes to rest during the first pivotal step against the front of the shuttle.

Also with the thread cutting means in accordance with the invention, still another stitch forming operation is effected after termination of the first pivotal step of the cutter. The needle thread which is guided about the looper shuttle now slides inevitably onto the guiding finger that closely contacts the front of the shuttle, then slides upwardly on the guiding finger and thus reaches the edge of the cutter. Due to the fact that in accordance with the invention the needle thread cutter itself has been equipped with a guiding element for the needle thread loop, it is immaterial whether the shuttle used in connection with the arrangement for thread cutting is provided with a bobbin capsule besides capsule retaining finger, or whether no bobbin capsule is present at all. It has thus become possible to utilize the means for thread cutting constructed in accordance with the invention for thread cutting not only in connection with central bobbin shuttles, but just as well also in connection with long beak shuttles.

The guiding finger is approached during the first rocking step of the cutters out of the position of rest in which is disposed at a lateral spacing with respect to the shuttle, to the front of the shuttle and is again removed from the shuttle during the course of the second rocking movement. The relative position between the arcuately shaped path of movement of the guiding finger and the front of the shuttle can here be compared with a circle and a tangent that is in contact therewith. Since the guiding finger does not reach into the path of movement of the shuttle and also not into the area in which the guidance of the shuttle extends, the thread cutting arrangement in accordance with the invention may therefore be employed in connection with standardized shuttles and standardized guide means for the shuttles.

Further details of the invention will become apparent from the following description of an embodiment illustrated in the drawings in which:

FIG. 1 is a front view of a sewing machine equipped with the thread cutting device in accordance with the invention,

FIG. 2 is a bottom view of the thread cutting device in position of rest,

FIG. 3 is a perspective illustration of the cutting device in the position immediately prior to the start of the second rocking step of the cutters, and

FIG. 4 shows the cutters in perspective illustration.

The sewing machine illustrated in FIG. 1 comprises a base plate 1, a standard 2 and an arm 3 which merges into the head 4. The armshaft 5 is journalled in arm 3. It is in driving connection with the needle bar 7 that is movable up and down in the head 4, and carries the needle 6. Furthermore, the take-up lever 8 is mounted in the head 4 and is driven by the armshaft 5.

Below the stitch plate 9 which has the stitch hole 10, the long beak shuttle 12 is disposed in the stationary guide 11 that is composed of two annular disks. The long beak shuttle 12 has a beak l3 and carries the bobbin 14 for the shuttle thread S. The long beak shuttle 12 is driven by way of driver 15 (FIG. 3) by means of the swinging shaft 16 which in a known manner is in driving connection with the armshaft by way of the arcuate pushing crank gear 17 (FIG. 1) and the drawbar 18.

The cutting mechanism has a support 19 rotatably disposed at the bottom of the stitch plate 9, and connected with a toothed gear 20. At the bottomside of the support 19 are secured a blade spring 21, a cutter 22 for the shuttle thread, as well as a cutter 23 for the needle thread. The cutter 22 for the shuttle thread has a catch hook 25 in the area of the point 24 and laterally thereof a low upwardly directed low cutting lip 26 having the edge 27. The cutter 23 for the needle thread supports an obliquely downwardly directed cutting finger 28 which is disposed in an essentially vertically downwardly directed guide finger 29. On the cutter 23 for the needle thread an angular cutting edge 30 for the needle thread is provided which is obtained by grind- The toothed gear 20 engages with an offset toothed bar 31 that has two elongated slots 32, 33 for guidance which are engaged by two head screws 34, 35 threadedly received in the base plate 1.

The toothed bar 31 is hingedly connected with a double lever 37 by means of a pin 36, and which is provided with two slots 38, 39 one each in the area of the opposite ends thereof. ln the slot 38 the pin 40 of a bifurcated head 41 is guided which is firmly connected with the drawbar 42 of an electromagnet 44 secured to the base plate 1 by means of a support 43.

On the drawbar 42 a pressure spring 46 is mounted between the support 43 and a setting ring 45. A pin 47 of a bifurcated head 48 is guided in the slot 39 and secured to the drawbar 49 of a second magnet 51 fastened by means of a support 50. On the drawbar 49 a pressure spring 53 is disposed between the support 50 and a setting ring 52.

The cutting mechanism operates as follows:

At the end of the seam the sewing machine is halted by a stopmatic motor that insures that the needle then is in the top position. Simultaneously, the circuit of the electromagnet 44 is closed. The magnet 44 now pulls up and thereby rocks the double lever 37 about the pin 47 of the forked head 48 that is at standstill which now serves as pivot point. By these means the toothed bar 31 is displaced in the direction of the two magnets 44, 51, the toothed gear 20 is rotated and the support 19 with cutters 22, 23 is pivotally moved counterclockwise out of the position of rest shown in FIG. 2 in the direction of the long beak shuttle 12.

During the course of this first rocking step, the point 24 of the cutter 22 for the shutter thread moves past under the stitch hole and seizes the shuttle thread S that rises from the bobbin 14 to the stitch hole 10. This thread thereby lays itself in the V-shaped recess between the point 24 and the catching hook 25. Simultaneously, also the guiding finger 29 of the cutter 23 for the needle thread moves toward the long beak shuttle l2 and at the end of the first pivot step engages the front of the long beak shuttle 12 in the manner shown in FIG. 3. The free end of the guiding finger 29 then contacts the long beak shuttle 12 in the proximity of the pivot axis of the long beak shuttle 12.

Upon completion of the first rocking step of the cutters 22, 23, there is still carried out a stitch forming operation. The loop of the needle thread N which is thereby guided around the long beak shuttle 12 now slides inevitably over the free end of the guiding finger 29, then slides upwardly on the guiding finger 29 onto the cutting finger 28 around which it slings itself closely at the end of its downward movement as shown in FIG. 3. At the same time the needle thread N pulls the shuttle thread S out of the originally straight line position between the catch hook 25 and the exit position 54 of the shuttle thread S from the long beak shuttle 12 into the angularly offset position illustrated in FIG. 3.

Now the circuit of the second electromagnet 51 is closed. This magnet pulls up and thereby rocks the double lever 37 about the pin 40 on the forked head 41 that now serves as pivot point which is standing still. Thereby, the toothed bar 31 is displaced a second time in the direction of the two magnets 44, 51. The toothed gear 20 is rotated and the support 19 with the cutters 22, 23 is rocked onward counterclockwise in the position illustrated in FIG. 3 in solid lines. In this connection, the cutters 22, 23 upon termination of this second rocking step assume the position illustrated in dot and dash lines in FIG. 3.

During the course of the second rocking step, the shuttle thread S slides first between cutter 22 for the shuttle thread S and leaf spring 21, then engages the cutting edge 27 of the cutting lip 26 and is finally severed thereby with a slashing cut. After the separating, the end of the shuttle thread S which is connected with the thread supply remains clamped between the cutter 22 for the shuttle thread and the leaf spring 21 and thereby assumes the position illustrated in dot and dash lines in FIG. 3. Like the shuttle thread S, also the needle thread N is severed by the edge 30 by a slashing cut.

With the cutting mechanism described, there result relatively long thread ends on the work blank. Sewing machines having long beak shuttles are used exclusively for working with relatively thick leather where the thread ends of a seam are glued onto the work blank in order to avoid that the seam is loosened. Therefore, it is advantageous when a mechanism for thread cutting used in connection with a long beak shuttle produces long thread ends on the work blank, because long thread ends can be glued on more securely than short ones. The ends of the shuttle thread S and of the needle thread N connected with their thread supply are sufficiently long to insure of a satisfactory interlacing of the thread at the beginning of a new seam.

Since the point 24 of the cutter 22 for the shuttle thread is moved above the guide means 11 of the long beak shuttle 12 and, since the guide finger 29 touches only the front of the long beak shuttle, neither the long beak shuttle 12 nor its guide means have to be changed in any manner for adaptation to the cutting arrangement.

With the arrangement for cutting threads in accordance with the invention only the measure of equipping the cutter 23 for the needle thread loop with a guiding element for seizingthe needle thread loop is decisive for always securely seizing the needle thread N. Thus, since the external form or type of the shuttle used in combination with the arrangement for thread cutting has no effect on the functioning ability of the means for cutting thread, the same can not only be utilized with long beak shuttles, but just as well also in connection with central bobbin shuttles.

Having now described our invention with reference to the embodiment illustrated in the drawings, what we tive to said shuttle thread cutter and having a guide finger for the loop of the needle thread, a drive means connected to said pivotable support for effecting a first rocking movement of said support to place said guide finger against the front of said shuttle and to seize the threads by means of the cutters, said drive means effecting a second rocking step of said pivotable support to cut the threads after the sliding of the needle thread loop onto the guide finger and the needle thread cutter. 

1. Thread cutting arrangement for lock stitch sewing machine comprising a stationary base and having a needle bar supporting a needle above said base, a shuttle pivotally supported for rocking movements and below said needle bar, a pivotably movable support having a vertical axis, a shuttle thread cutter, and a needle thread cutter disposed on said support and spaced relative to said shuttle thread cutter and having a guide finger for the loop of the needle thread, a drive means connected to said pivotable support for effecting a first rocking movement of said support to place said guide finger against the front of said shuttle and to seize the threads by means of the cutters, said drive means effecting a second rocking step of said pivotable support to cut the threads after the sliding of the needle thread loop onto the guide finger and tHe needle thread cutter. 